The present invention relates generally to data processing systems, and particularly to a direct access storage system with a combined block interface and file interface access.
Interconnecting the various elements of a processing system (e.g., processor units and peripheral equipment such as direct access storage devices) permits the resources of the system to be distributed so that they are available to all elements of the system. For example, multiple processor units may be connected to a storage system for sharing not only the afforded storage space, but the files that are stored there. Typically, a network architecture of one type or another will be used to implement the interconnection, which may dictate the particular of interface structure between the elements of a system, e.g., a processor unit and a data storage system. For example, it has been popular to connect stand-alone processor units to a direct access storage devices using a small computer standard interface (SCSI). SCSI connections use block transfer protocols in which a logical unit number (LUN) identifies the logical volume for access.
Network protocols, on the other hand, are different. Protocols of choice for networked and distributed processing systems included Network File System (“NFS;” an open operating system developed by Sun Microsystems), a Common Internet File System protocol (“CIFS;” a remote file access protocol), or a HyperText Transport Protocol, more popularly known as “HTTP.” These protocols use what is known as a “file system interface,” and while the file interface structures used to implement the different file system interface protocols, they use a common file system structure. Thus, data stored on a storage system using a file system interface of two or more types are available to all host systems. For example, a storage system capable of handling input/output requests of both NFS and CIFS protocols, i.e., an NFS protocol interface and a CIFS protocol interface, can store data files that are accessible to host processors having either of the NFS interfaces. That is, a host system with only an NFS interface can access and open files stored by a host system with a CIFS interface, and the host system with a CIFS interface can access and open files stored by the system via the NFS interface—provided the storage system has both interfaces.
Storage systems having one or more of the file system interfaces of the types described above provide access through an I/O read or write request that includes a file name, and an lock request that seeks a right to access the particular file of the I/O request.
Most direct access storage systems have either a block interface or a file interface, and host systems using a block interface protocol cannot access storage systems employing file interface protocols. Further, because of the differences between block and file interface structures and the way data is stored and accessed, a storage system is structured for a block system or a file system, but not both.
Remote replication is a backup technique that is used for data recovery scenarios such as disaster recovery. As a typical example, considers a RAID based storage configuration. A primary data side will have a first RAID controller for data access in a first RAID storage component. A second RAID controller at a secondary data site is provided for data backup in a second RAID storage component. The two RAID controllers are typically connected to each other via a communication network. Data in a primary volume in the first RAID storage component presented by the RAID controller at primary site can be replicated to a secondary volume in the second RAID storage component presented by the RAID controller at secondary site. When a write request to the primary volume is received by the first RAID controller, it sends the data update directly to the second RAID controller with no server involvement. This replication functionality is also referred to as “remote copy.” e.g., Hitachi TrueCopy™. Conventional RAID controllers have block system interfaces such as Fibre Channel and so are connectable to a storage area network (SAN). However, such controllers cannot connect to a network attached storage (NAS) device since they do not support file system I/O. Hereinafter, a storage system that is attachable to a SAN and which does not have a file system is referred to a SAN device.
Some NAS devices also provide replication capability for disaster recovery or other purpose. For instance, Network Appliance™ SnapMirror™ software replicates data on one or more network filers over a LAN or WAN and continuously updates the replicated data.